The invention relates in general to an end mill for orbital hole drilling, and in particular to an end mill having a forward cutting end with a radiused or convexly curved section that minimizes the accumulation of material from the workpiece to enable smooth drilling of the workpiece material, especially in layered materials without separating the layers.
Orbital drilling is a holemaking operation by milling in which the center of an end mill orbits about the center of the intended hole while spinning on its own axis and moving in the axial direction. Orbital drilling is also known as circular milling or helical interpolation.
Referring now to FIG. 7, a conventional end mill for orbital drilling is shown. The end mill 100 includes has a shank 102, a neck 104, a cutting head 106, and a longitudinal axis 108. In general, the neck diameter 112 is less than the shank diameter 110 and the cutting diameter 114. As shown in FIG. 8, the cutting head 106 includes a forward cutting end 116 that includes a dish angle 118 with respect to the end face. The cutting head 106 also includes a corner radius 120, and a flat 122 that extends from the corner radius 120 to a back radius 124 that causes reduction in diameter from the cutting head 106 to the neck 104.
As shown in FIGS. 9 and 10, a conventional non-center cutting end mill 200 includes four flutes, 202, 204, 206, 208 formed at a helix angle 210. In addition, the end mill 200 includes an end teeth radial rake angle 212, a gashing axial rake angle 214, and a primary clearance angle 216. Typically, the end teeth radial rake angle 212 is approximately equal to a peripheral teeth radial rake angle 218.
During an orbital drilling operation, the cutting head 106 of the end mills 100, 200 first come into contact with the workpiece at an initial contact area 126, 226, respectively, which is proximate the corner radius 120. Because of the dish angle 118, the material being removed by the end mill 100, 200 tends to travel radially inward toward the longitudinal axis 108 and accumulate in a central portion 106a of the cutting head 106. The material also tends to mostly accumulate along the longitudinal axis 108 and accumulate less near the corner radius 120.
As a result of this accumulation of material on the cutting head, the performance of the conventional end mill suffers. Thus, there is a need to provide a cutting tool that minimizes the accumulation of material during an orbital hole drilling operation.